1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor optical device, and more particularly to a method for manufacturing a semiconductor optical device in such a way that the operating resistance of the device does not deviate from the design value.
2. Background Art
Semiconductor lasers have been widely used in optical disc drives, scanners, copiers, etc. JP-A-11-307810 (1999) discloses such a semiconductor laser, which has two important features. First, this semiconductor laser includes a BDR (Band Discontinuity Reduction) layer disposed between a contact layer and a cladding layer to reduce the band discontinuity between these contact and cladding layers and thereby reduce the device resistance. This BDR layer has an energy bandgap intermediate between the energy bandgaps of the contact layer and the cladding layer. Second, the contact layer is doped with C to reduce the contact resistance between the contact layer and the electrode. Other prior art includes JP-A-2005-85848, JP-A-10-308551, and JP-A-2001-144322.
In conventional semiconductor lasers such as described above, impurities doped into the BDR layer may diffuse into the contact layer due to heat applied during and after the contact layer growth process. This thermal diffusion leads to a reduction in the impurity density of the BDR layer and hence an increase in the operating resistance of the semiconductor optical device, with the result that the operating resistance of the device deviates from the design value.